Messages in this thread |  | | | Date | Thu, 07 Feb 2008 09:37:12 -0800 | | From | "H. Peter Anvin" <> | | Subject | Re: 2.6.24 says "serial8250: too much work for irq4" a lot. | |
Ingo Molnar wrote:
> * H. Peter Anvin <hpa@zytor.com> wrote:
>
>>> (If it's a qemu issue, I can go bother them. It's possible that qemu
>>> isn't delivering interrupts as often as it expects, since that's
>>> limited by the granularity of the host timer; I know the clock in
>>> qemu can run a bit slow because it only gets clock interrupts when
>>> the host system isn't too busy to schedule the emulator. But this
>>> doesn't usually cause a problem. I _think_ the message is just a
>>> "this should never happen" type warning, which is happening to me.
>>> But I break stuff. :)
>> This is because Qemu spews data to the serial port without any rate
>> limiting; this causes the in-kernel serial port driver to think the
>> port is stuck. The serial port emulation needs to make it possible to
>> drain the virtual FIFO every now and then, as opposed to filling it
>> again immediately.
>
> actually, the way i solved it for qemu+KVM+paravirt was to just turn off
> this rather silly check in the serial driver if inside a paravirt guest.
> When we are emulated then the serial 'hardware' is totally reliable and
> we should just trust it. That way i never dropped a single bit of kernel
> log output again.
>
Yes, but keying that on paravirt is silly in the extreme. After all,
there is no need for this to be paravirtualized.
-hpa
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